Is soya a has-bean?

By PETA BEE, Daily Mail

Last updated at 15:51 25 May 2006

For years it's been hailed as a superfood. Now doctors are asking just how good for you soya really is. Good Health investigates

Soya was the 'wonderbean' when it emerged onto the food scene ten years ago. The legume's health benefits appeared limitless, from boosting bone strength and relieving menopausal symptoms to preventing breast cancer and lowering cholesterol.

Suddenly, soya, a staple of Far Eastern diets for centuries, was everywhere.

Today you can eat soya-enriched breakfast cereals and chocolate, cook soya sausages or tofurkey, a soya-meat substitute, and indulge in soya ice cream or yogurt. Soya is now so mainstream you even buy a soya milk latte at High Street coffee shops.

Soya-based drinks are the fastest growing food category worldwide, according to a recent American survey, while in the UK, the market for soya meat alternatives alone is worth £77million a year. Almost 30 per cent of us eat soya-containing foods once a week.

While best-sellers include tofu and soya milk, enthusiasts buy increasing amounts of tempeh and edamame, traditional Asian forms of soya, along with soya-based powders and supplements.

But a growing number of consumer pressure groups and experts claim there is mounting evidence that soya is not healthy, and might even, in some instances, be bad for you.

The concern is that soya contains large quantities of chemicals that cannot be fully destroyed even by a long cooking process. These chemicals include enzyme inhibitors, which hamper protein digestion, phytates, which block the absorption of minerals, and haemagglutin, which hinders the body's use of oxygen.

More worrying, it seems, is that soya contains high levels of genistein and daidzein, which mimic the female sex hormone oestrogen and may affect development and fertility.

Scientists from King's College, London, revealed soya is far from a magic bean when it comes to helping women conceive. Professor Lynn Fraser said chemicals in soya could prevent sperm binding with an egg.

Advice: restrict your diet

After adding genistein to sperm samples, she found it had a negative effect. For women who are trying to get she advised: "It might practical, if you eat a lot of soya-based products, to restrict your diet for a short period over your window of ovulation."

Even the Vegetarian Society went along with this advice, saying: "For anyone struggling to become pregnant, avoiding soya products for a few days a month is worth a try."

Previously, the low rates of cancer — breast, uterus, colon and prostate — among the Japanese has been linked to the high soya-content of their diets. But even that is not clear-cut.

A 1998 study showed that a Japanese man typically eats about 8g a day, nowhere near the 220g that a Westerner could put away by eating a big chunk of tofu and two glasses of soya milk.

And while the Japanese do have lower rates of these cancers, some experts suggest this is due to other factors: they eat less fatty meat, more fish and vegetables and fewer processed foods than people in the West.

More convincing, perhaps, was the evidence for soya's heart-health benefits. A couple of years ago, the UK's Joint Health Claims Initiative, an independent consumer and trading standards panel, gave the go-ahead for manufacturers of soya-rich foods to make claims about their products' heart-protecting benefits.

After reviewing more than 50 studies, experts agreed that consuming 25g of soya protein daily, as part of a diet already low in saturated fat, may help reduce the risk of heart disease.

The research, carried out over 25 years, showed how eating soya regularly can lower overall cholesterol by an average 9 per cent and result in a 13 per cent drop in levels of the unhealthy LDL-type cholesterol that clogs the arteries.

Soya is also approved as a heart-healthy food by America's Food and Drug Administration.

Yet in January, the American Heart Association (AHA) published an advisory document retracting earlier advice about "including soya protein foods in a diet low in saturated fat and cholesterol".

A review of 22 studies showed soya protein with isoflavones did not seem to lower cholesterol and, the AHA felt it could not "recommend the use of isoflavones in pills or food for the prevention of heart disease".

In its own statement, the British Heart Foundation agrees that soya has only a minimal effect on lowering 'bad' LDL cholesterol and "has no significant effect on 'good' cholesterol, triglycerides and blood pressure".

Last month came more bad news for soya. A study in the Journal of the National Cancer Institute showed that, although soya slightly lowered the risk of breast cancer, it was not significant enough to recommend that women consume soya food or supplements.

Soya 'risky' for breast cancer survivors

For breast cancer survivors, says Professor Leena Hilakivi-Clarke, who led the study at Georgetown University's centre, soya supplements could be positively risky as they contain higher amounts of oestrogen-like isoflavones that "coax breast tumour cells to divide and multiply".

Even the evidence for soya reducing menopausal symptoms seems to be eroding. Early studies found it reduced hot flushes by up to 40 per cent, but later trials have shown little effect.

But Professor Aedin Cassidy of the school of medicine at the University of East Anglia, a leading researcher into the effects of soya, says that many of the negative findings about soya are being overplayed.

"Most of the risks are hypothetical as tests have been carried out on species other than humans,' she says. 'What we do know is that the source of soya is hugely important. Soya foods are far more effective than soya supplements."

In one of her studies, Cassidy found that a lifelong soya consumption reduced the risk of breast cancer in women. "It is not an unhealthy food, and there is no need to cut it from your diet," she says. As with all things, the key is moderation.